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A key challenge is to realize ultracompact lasers that can directly generate coherent optical fields at the nanometre scale, far beyond the diffraction limit. Surface plasmons could be used to tightly confine light on very short lengthscales, but so far this approach has been hampered by ohmic losses at optical frequencies. The experimental demonstration of nanometre-scale plasmonic lasers is now reported, realized using a hybrid plasmonic waveguide — these lasers can generate optical modes a hundred times smaller than the diffraction limit.

Metal-based nanostructures offer a solution to scale down photonics to the nanoscale. Sorgeret al. directly demonstrate waveguiding of ultra-small propagating waves at visible and near-infrared frequencies using NSOM imaging, with the potential for nanoscale photonic applications such as bio-sensing.

Plasmon lasers can operate at dimensions well below the diffraction limit. Their small size promises uses in nanophotonic circuits and for other size-critical applications. The demonstration of a sub-diffraction-limited plasmon laser with low losses, which enables its room-temperature operation, takes a significant step towards realizing the potential of these lasers.

Photon Bose–Einstein condensation is observed in a semiconductor laser, where thermalization and condensation of photons occur using an InGaAs quantum well and an open microcavity. The distinction between regimes of photon Bose–Einstein condensation and conventional lasing are clearly identified.

A planar composite material images ultraviolet light like a lens, by unwinding its phase. The concept could aid high-resolution nanolithography.

Emission enhancement and extraction from quantum emitters is a major challenge for photon sources in e.g. quantum photonic networks. Here the authors propose a broadband waveguide platform which allows to boost, extract, and guide quantum emission within integrated photonic networks.

Providing sufficient gain to overcome loss remains a fundamental challenge for light amplification in miniaturized plasmonic devices. Ongoing research gives hope for a cautious but optimistic outlook.

Extending magnetic nanostructures into three dimensions offers a vast increase in potential functionalities, but this typically comes at the expense of ease of fabrication and measurement. Here, Dion et al. demonstrate an approach to creating three dimensional magnetic nanostructures while retaining easy fabrication and readout of established two dimensional approaches.

Absorption by an optical nanoantenna determines its interaction strength with light, yet this quantity is hidden from conventional spectroscopy. Gennaro et al. now demonstrate a spectroscopic technique that reveals a nanoantenna’s absorption by recovering its amplitude and phase response.

Electron scattering limits the optical excitations produced by metal-based lasers to femtosecond timescales. But sub-picosecond pulsing can be achieved in a plasmonic nanowire laser by operating near the surface plasmon frequency.

Description of non-equilibrium phase transitions is problematic, due to the absence of suitable free energy landscapes. Here, the authors experimentally show delayed photon condensation and timing jitter in a dye-filled microcavity, modelled by a non-equilibrium extension of the free-energy landscape.

Metallic nanoantennas can enhance and confine electromagnetic fields, however, localized heating hinders many applications. Here, Caldarola et al.demonstrate both high near-field enhancement and ultra-low heat conversion in the visible-near infrared region using silicon dimer nanoantennas with 20 nm gaps.

The photoresponse of graphene-based photodetectors is dominated by photovoltaic and photothermoelectric effects. Here, the authors leverage strongly localised plasmonic heating of graphene carriers to detect a second photothermoelectric effect occurring across a homogeneous channel in the presence of an electronic temperature gradient.

Multilayered ferroelectric NbOI₂ crystals with sub-100-nm thickness exhibit efficient second harmonic generation, paving the way for on-chip nonlinear optical components.

Raman scattering within plasmonic waveguides is found to be directed into a single mode with near-unity efficiency, offering a route to broadband SERS enhancements over extended sensing volumes.

Since the first proposal for plasmonic nanolasers there has been a debate about the limitations on performance posed by the inherent losses in metallic systems. Here, the authors compare over 100 plasmonic and photonic laser devices and find sub-wavelength plasmonic lasers to be advantageous.

We experimentally demonstrate high-quality infrared imaging ranging from >1000 to 4000 nanometers with Si metasurfaces based on four-wave mixing (FWM) processes, by employing a pump beam at resonant position.

This Review highlights the fundamental advantages of nanolasers and the engineering challenges for their utilization in several practical applications.